Conventionally, a reflecting plate prepared by applying a coating material excellent in light reflection property to a metallic plate and a reflecting plate prepared by laminating resin films and the like excellent in the light reflection property on a metallic plate have been used as a reflecting plate of a light and liquid crystal back light. In recent years, power saving and high efficiency have been more required in fields such as a lighting apparatus and a liquid crystal display. In particular, needs for space saving has been enhanced in fields such as an electrical spectacular sign and a display. However, it is hard for the above described reflecting plates to tackle the space saving.
Accordingly, a resin sheet that is excellent in the light reflection property and has fine bubbles (for example, around 1 μm) has been used as a reflecting plate and the like of the light and the liquid crystal back light (for example, see Patent Literature 1). However, since the resin sheet described in Patent Literature 1 is prepared by foaming polyethylene terephthalate that is a crystalline resin, problems in moldability could have occurred.
On the other hand, a foam using an amorphous resin without using a crystalline resin is excellent in the moldability; however, not only fine bubbles but also coarse bubbles with a size of 1 mm or more are easily generated upon foaming, and thus, such a resin had a problem of difficulty in use as various molded articles such as a light reflecting material.
Then, an amorphous thermoplastic resin sheet having a uniform bubble diameter by foaming at less than a glass transition temperature (Tg) of an amorphous thermoplastic resin is proposed (for example, see Patent Literature 2). However, when such an amorphous thermoplastic resin is foamed at a temperature lower than Tg, an expansion ratio is not improved, and thus, not only desired performance is hardly attained but the cost is also disadvantageous.